Scientists have discovered that reduced krill supplies result in fewer humpback whale pregnancies, which could have major implications for industrial krill fishing.
Data from Antarctica show that humpback whales become pregnant more frequently after years of abundant krill than after years of scarcity.
Influence of Krill Availability on Humpback Whale Pregnancies
LOIC VENANCE/AFP via Getty Images
The study, which was published in the journal Global Change Biology on January 15, is based on eight years of data on humpback whale pregnancies (2013 to 2020) in waters along the Western Antarctic Peninsula, where krill fishing is concentrated, as per ScienceDaily.
The availability of krill in the year preceding a humpback pregnancy is critical because females need to build up their energy reserves to support the upcoming pregnancy.
In 2017, after a year of abundant krill, 86% of the humpback females sampled were pregnant.
However, only 29% of humpback females were pregnant in 2020, following a year with fewer krill.
The study, according to lead author Logan Pallin, a postdoctoral researcher in the Ocean Sciences Department at UC Santa Cruz, establishes for the first time a link between population growth and krill availability in Antarctic whales.
This is significant because it was previously thought that krill were an almost limitless food source for whales in the Antarctic, according to Pallin, who earned his Ph.D. in ecology and evolutionary biology at UCSC while working on this study.
Warming temperatures and increased fishing along the Western Antarctic Peninsula, which are reducing krill stocks, are likely to have an impact on this humpback whale population and other krill predators in the region.
The Western Antarctic Peninsula, according to coauthor Ari Friedlaender, professor of ocean sciences at UC Santa Cruz, is experiencing some of the fastest climatic warmings of any region on the planet.
Winter air temperatures have risen significantly since the 1950s, and annual sea ice extent is now 80 days shorter on average than it was four decades ago.
Because juvenile krill feed on algae growing on sea ice and also rely on the ice for shelter, years with less sea ice in the winter result in fewer juvenile krill surviving the following year.
Climate change and, most likely, the krill fishery are both contributing to a decrease in humpback whale reproductive rates in years when there is less krill available for whales.
According to coauthor Chris Johnson, global lead of the World Wide Fund for Nature's Protecting Whales and Dolphins Initiative, this research shows that highly precautionary management measures are required to protect all Antarctic marine life that depends on krill for survival, including blue, fin, humpback, minke, and southern right whales, as well as other krill predators like penguins, seabirds, seals, and fish.
Krill is not an infinite resource, and there is an increasing overlap between industrial krill fishing and whales feeding at the same time, according to Johnson.
Humpback whales feed in the Antarctic for a few months each year to meet their annual energy requirements for thousands of kilometers of migration.
We must tread carefully and protect this one-of-a-kind area of the world, which will benefit whales throughout their entire range.
In the baleen whale suborder, humpback whales have a fairly diverse diet that includes small fish, krill, salmon, herring, mackerel, and capelin, among other small prey, as per Whale Facts.
Because the humpback lacks teeth and must swallow its food whole, these marine mammals can only eat small aquatic animals.
During the summer, these whales hunt and feed in cold waters, and during the winter, they migrate to warmer tropical areas to mate and bear offspring.
During the humpback feeding season, these whales hunt using a technique called bubble net fishing, which involves a group of humpback whales swimming in a circle around their prey and blowing bubbles around the fish to herd the fish into a tight ball.
The whales will also make loud vocalizations to scare the fish to the surface of the water and slap their fins against the water to stun and immobilize them.
When the fish are unable to move, the whales will swim up and lunge at them with an open mouth, engulfing hundreds or thousands of small fish in a single gulp while using their baleen bristles to separate the water and debris from their prey.
After capturing a mouthful of fish, the humpback will use its tongue to push the water out of its mouth and swallow the remaining prey.
During feeding season, humpback whales feed frequently and build up their blubber stores in preparation for mating season.
During mating season, humpback whales will fast (stop eating) and live off of body fat/blubber reserves acquired during feeding season in order to focus on migration and mating.
